Java Practical info : Inter Servlet Communication?

What are Servlet Filters

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                      
Hello everyone I think everyone celebrate NEW YEAR and Every one
welcoming 2013. I hope this year give lot of joeys and what are dreams in your
mind comes into true. Now see current post is related to filters. My last post I
given some of the Servlet information. Please see all servlet related post
once.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                    A filter is a container managed object that is declarative
inserted within the request-response cycle of http client and http server. A
filter instances acts as an interceptor. It is a preprocessed of the request
befre it reaches a servlet and a post processor of the response leaving the
servlet. A filter can perform the following.<o:p></o:p></span></div>
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<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Intercept a servlet’s invocation before a
servlet is called.<o:p></o:p></span></div>
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<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Examine the request before a servlet is called.<o:p></o:p></span></div>
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<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Modify the request headers and request data.<o:p></o:p></span></div>
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<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Modify the response headers and response data.<o:p></o:p></span></div>
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<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Intercept a servlet’s invocation after the servlet
is called.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">               A filter object implements <i>javax.servlet.Filter.interface</i>. The interface provides 3 life cycle
methods.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Public void
init(FilterConfig):-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> Servlet engine calls this method only once
after instantiating the filter. Initialization parameters are encapsulated in
the FilterConfig object. By calling getInitParameter method in the
FilterConfing object we can retrieve them. This method must complete successfully
before the filter is asked to day any filtering work.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Public void
doFilter(ServletRequest,ServletResponse,FilterChain):-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> It is
called by the container each time a request/ response pair is passed through
the chain due to a client request for a resource at the end of the chain. The
FilterChain passed into this method allows the filter to pass on the request
and response to the next entity in the chain.<o:p></o:p></span></div>
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<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Public void
destroy():-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> Called by the servlet engine to indicate to a
filter that it is being taken out of service. This method gives the filter an
opportunity to clean up any resources that are being held. For example, closing
of the database connection.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            Hey common
you know my principle why you need to study all the mater right just watch the following
video you can understand better way what are the Servlet Filters, right then why late start the following
video. Once again HAPPY NEW YEAR 2013. <o:p></o:p></span><br />
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What are Servlet Filters

Image Source Google Images Hello everyone I think everyone celebrate NEW YEAR and Every one welcoming 2013....

Session Tracking

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                                 This post is regarding Session
Tracking information previous post totally servlet related information and what
are the types of servlets your all seen right now what is the session Tracking
you can know much very easy way okay lest start.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                             Http is stateless protocol. A web client opens a
connection with the http server and requests some resource. The server responds
with the requested resource and closes the connection with client. After
closing the connection, the http server does not remember any information about
the client. The server considers the next request from the same client as a
fresh request, with no relation to the previous request. This is what the
stateless nature of the Http protocol.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                                In enterprise web application it is mandatory that client
and its associated data must be tracked at server side across multiple
requests. There are four approaches to achieve this.<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;">v<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Hidden
form fields<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;">v<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Cookies<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;">v<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Session
tracking with Servlet API<o:p></o:p></span></div>
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<span style="font-family: Wingdings; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Wingdings; mso-fareast-font-family: Wingdings;">v<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  </span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">URL
rewriting<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Note: for Hidden form fields mechanism there is no servlet
API support available.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Georgia; mso-fareast-font-family: Georgia;">1.<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">              <b><u> </u></b></span></span><b style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;"><u>Hidden
form fields:-</u></b><span style="font-family: Georgia, serif; font-size: small;"><span style="line-height: 115%;">a hidden field is similar to an ordinary input field in HTML. The
only difference is that the hidden field </span></span><span style="font-family: Georgia, serif;"><span style="line-height: 18.18181800842285px;">doesn't</span></span><span style="font-family: Georgia, serif; font-size: small;"><span style="line-height: 115%;"> have an associated user
interface element. When the form that contains these hidden form fields is
submitted, the values of these fields are sent with the request. On the server side,
these values are received as request parameters. This mechanism works only when
form is submitted, not when you click the hyperlink. The key point is that
client in this mechanism. That is how state is managed across multiple
requests. In J2EE environment this mechanism is not so widely used, as there is
no Servlet API support available.<o:p></o:p></span></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">         Hey
common I don’t want to give Para’s matter here. I can show you video’s for
better understand that why I am giving here let see why you are late.<o:p></o:p></span></div>
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Session Tracking

This post is regarding Session Tracking information previous post totally servlet related information ...

Servlet Error Handling

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                                         Hi All
Everyone is enjoyed Christmas festival still some part of the world celebration
going up to New Year. Any have spent some valuable time to see my blog also for
this thanks lot. I am trying to give some information regarding Servlet
Exception Handling. In Every Application Development you must raise some un
excepted error may occurred. Sometimes you need to handle Exception for end
user point of you, so in order to use servlet you need to handle exception in
the following different ways. Any one of the technique you can implement some
times more than one technique also allows.  Now the time to see the different Techniques.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%; mso-bidi-font-family: Georgia; mso-fareast-font-family: Georgia;">1.<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">      
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">When a servlet throws an exception, the web
container searches the configurations in web.xml that use the <b>exception-type</b>
element for a match with the thrown exception type.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">You would have to use the error-page element in web.xml to specify the invocation
of servlets in response to certain exceptions or HTTP status codes.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Consider, you have an ErrorHandler servelt which would be called whenever there
is any defined exception or error. Following would be the entry created in <b>web</b>.xml.<o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><servlet><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">       
<servlet-name>ErrorHandler</servlet-name><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">       
<servlet-class>ErrorHandler</servlet-class><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></servlet><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><servlet-mapping><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">       
<servlet-name>ErrorHandler</servlet-name><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">       
<url-pattern>/ErrorHandler</url-pattern><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></servlet-mapping><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<error-code>404</error-code><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<location>/ErrorHandler</location><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<error-code>403</error-code><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<location>/ErrorHandler</location><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">    <exception-type><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">         
javax.servlet.ServletException<o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">    </exception-type ><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<location>/ErrorHandler</location><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"><error-page><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<exception-type>java.io.IOException</exception-type ><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">   
<location>/ErrorHandler</location><o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;"></error-page><o:p></o:p></span></div>
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<br /></div>
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<span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">2.<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">     
</span></span><span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">If you want to have a generic
Error Handler for all the exceptions then you should define following
error-page instead of defining separate <b>error-page</b>
elements for every exception:</span><o:p></o:p></div>
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<br /></div>
<pre style="background: #F1F1F1;"><span style="font-family: Georgia, serif; font-size: 12pt;"><error-page><o:p></o:p></span></pre>
<pre style="background: #F1F1F1;"><span style="font-family: Georgia, serif; font-size: 12pt;">    <exception-type>java.lang.Throwable</exception-type ><o:p></o:p></span></pre>
<pre style="background: #F1F1F1;"><span style="font-family: Georgia, serif; font-size: 12pt;">    <location>/ErrorHandler</location><o:p></o:p></span></pre>
<pre style="background: #F1F1F1;"><span style="font-family: Georgia, serif; font-size: 12pt;"></error-page><o:p></o:p></span></pre>
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<span style="font-family: Georgia, serif; font-size: 12pt;">Following are the points to be
noted about above web.xml for Exception Handling:<o:p></o:p></span></div>
<ul type="disc">
<li class="MsoNormal" style="background-color: white; background-position: initial initial; background-repeat: initial initial; text-align: justify;"><span style="font-family: "Georgia","serif"; font-size: 12.0pt; mso-bidi-font-family: "Courier New"; mso-fareast-font-family: "Times New Roman";">The servelt ErrorHandler is defined in
     usual way as any other servlet and configured in web.xml.<o:p></o:p></span></li>
<li class="MsoNormal" style="background-color: white; background-position: initial initial; background-repeat: initial initial; text-align: justify;"><span style="font-family: "Georgia","serif"; font-size: 12.0pt; mso-bidi-font-family: "Courier New"; mso-fareast-font-family: "Times New Roman";">If there is any error with status code
     either 404 ( Not Found) or 403 ( Forbidden ), then ErrorHandler servlet
     would be called.<o:p></o:p></span></li>
<li class="MsoNormal" style="background-color: white; background-position: initial initial; background-repeat: initial initial; text-align: justify;"><span style="font-family: "Georgia","serif"; font-size: 12.0pt; mso-bidi-font-family: "Courier New"; mso-fareast-font-family: "Times New Roman";">If the web application throws either ServletException or IOException,
     then the web container invokes the /ErrorHandler servlet.<o:p></o:p></span></li>
<li class="MsoNormal" style="background-color: white; background-position: initial initial; background-repeat: initial initial; text-align: justify;"><span style="font-family: "Georgia","serif"; font-size: 12.0pt; mso-bidi-font-family: "Courier New"; mso-fareast-font-family: "Times New Roman";">You can define different Error
     Handlers to handle different type of errors or exceptions. Above example
     is very much generic and hope it serve the purpose to explain you the
     basic concept.<o:p></o:p></span></li>
</ul>
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<span style="font-family: Georgia, serif; font-size: 12pt;">3.<span style="font-family: 'Times New Roman'; font-size: 7pt;">      </span></span><b><span style="font-family: Georgia, serif; font-size: 12pt;">Request Attributes - Errors/Exceptions</span></b><span style="font-family: Georgia, serif; font-size: 12pt;">:<o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt;">Following is the list of request
attributes that an error-handling servlet can access to analyses the nature of
error/exception.<o:p></o:p></span></div>
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<span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">Hey common I am not forced to
read entire thing here you know my motive right I am stopping here to give much
please see the following video you can understand better way .<o:p></o:p></span><br />
<div style="text-align: center;">
<span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;"><br /></span></div>
</div>
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<span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">        </span></div>
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Servlet Error Handling

Hi All Everyone is enjoyed Christmas festival still some part of the world celebration going up ...

What is Deployment Descriptor?

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                           Hello everyone my
last post one small HelloWorld Example I am showed in the video. This just for awareness
of the servlet based application. In the last I didn’t mention deployment descriptor
information in that now I am trying to give here deployment descriptor types
and what is the use of deployment descriptor.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                        Deployment Descriptor
is a component in Java EE application that describes how a web application
should be deployed. It is an xml file provided with each module of the
application. It describes the configuration information for that module. It must
e placed in WEB-INF directory, directly under the web application root. There are
different kinds of deployment descriptor. Hey common I am giving these
information into video while reading some people may not interest just simply relax
and see video is enough that the reason I am giving here video why your late
let see the video <o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Like that we can add the
following information in deployment descriptor.<o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><servlet><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            <servlet-name>ShowRequestHeaders</servlet-name><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            <servlet-class> ShowRequestHeaders</servlet-class><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"></servlet><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><servlet-mapping><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            <servlet-name> ShowRequestHeaders</servlet-name><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            <url-pattern>/req</url-pattern><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"></servlet-mapping><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"></web-app><o:p></o:p></span></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Add more number of deployment
descriptor elements while using EJB in the application.<o:p></o:p></span></div>
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<br /></div>
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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Next post on Request and
Response Headers…………….<o:p></o:p></span></div>
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What is Deployment Descriptor?

Hello everyone my last post one small HelloWorld Example I am showed in the video....

HelloWorld Servlet Example

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<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">                     </span><span style="font-size: 12pt; line-height: 115%;"><span style="font-family: Georgia, Times New Roman, serif;"> Hello Every one in this post 
I am trying to develop one simple HelloWorld servlet application. Here
also I am showing these steps through video. Please watch each step by step and
implement in your system I know you never forgot any single piece of step. Here
I am telling one there is lot of open source and books and many more available
I am not blamed any one there is different kind of approaches. I feel this is
one kind of approaches you may like or dislike. But one think I tell once I can
read any story it may lost after few days if you implement those reading
concepts or visualizing you never forgot right friends.<o:p></o:p></span></span></div>
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<span style="font-size: 12pt; line-height: 115%;"><span style="font-family: Georgia, Times New Roman, serif;"><br /></span></span></div>
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<span style="font-size: 12pt; line-height: 115%;"><span style="font-family: Georgia, Times New Roman, serif;">                        In
my previous post how many type of servlets available. What are the methods we
need to implement, what is the syntax kind of information you understand. Now
the time is understanding points implementation time right see the following
video and implement step by step. Hello friends one thing I can tell you better
to practice once after see this, if you feel its not understanding better to
see twice and implement after your confidence level defiantly increased.</span><span style="font-family: Georgia, serif;"><o:p></o:p></span></span></div>
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<a class="g-profile" href="http://plus.google.com/113781836164165339620" target="_blank">+Chandra Sekhar</a>          Next post we will much more details about servlets...............<br />
<br /></div>
</div>

HelloWorld Servlet Example

Hello Every one in this post I am trying to develop one simple HelloWorld servlet application. Here also I am sho...